Gas electrodes, in which a gas is bubbled over a suitable conductor immersed in an electrolyte solution are well known. Such assemblies even find occasional application for use as reference electrodes.
In the configuration described, the actual relative utility for either galvanic (as, for example, in battery arrangements) or electrolysis (as, for example, in chlor-alkali processes with salt brine) operations is usually quite limited due to the ordinarily low current densities ordinarily therewith obtained.
Many types and varieties of porous and generally catalytically-active electrodes have been developed and are available which are intended and designed to current density realizations. This is effected by means and virtue of physical structuring that is characterized in presenting high actual electrode surface area within and throughout the confines of a reasonably- and practically-sized body insofar as spatial requirements for externally exposed area and apparent body volume are concerned. Electrodes so styled are designed with the premise, calculated to provide practical current density obtention in and through the electrode, of achieving bilateral mutually partial penetration into the interstices of the porous, electroconductive, catalytic body structure of electrolyte solution from and into one side of the body and reactive gas (such as one consisting or comprised of hydrogen or oxygen and so forth) from and into the other side of the body so that the oppositely ingressing, heterogenously-phased gas and liquid components form an interface within substantially entirely if not all of said interstitial passageways.
Electrochemical reaction then occurs within the porous electrode. In the case of fuel cells and other types of battery assemblies wherein appropriate anode, cathode and electrolyte selections are involved, useful electrical power generation is had. In cells for electrolysis wherein choice of appropriate electrolyte(s) is made along with suitable picking of anode and cathode for the system, useful products of the transformed anolyte and/or catholyte are obtained.
Various aspects relevant to the use of gas electrodes in galvanic and electrolysis mode applications, including oxygen depolarized cathodes in electrolytic cells, are amply demonstrated in, inter alia, U.S. Pat. Nos. 1,474,594; 2,273,795; 2,680,884; 3,035,998; 3,117,034; 3,117,066; 3,262,868; 3,276,911; 3,316,167; 3,377,268; 3,507,701; 3,544,378; 3,645,796; 3,660,255; 3,711,388; 3,711,396; 3,767,542; 3,864,236; 3,923,628; 3,926,769; 3,935,027; 3,959,112; 3,963,592; 4,035,254; and 4,035,255; and Canadian Patent No. 700,933; all and all therein being herein incorporated by reference. A demonstration of a porous, flow-through electrode appears in the literature in an Article by H. Khalifa et al. entitled "Electrochemical Reduction of Oxygen At A Porous Flow-Through Electrode" in J. Electroanal. Chem., 81 (1977) 301-307.
Such electrodes which utilize oxygen and are known as oxygen gas-bearing depolarized electrodes are of especial interest in chlor-alkali operation and analogous electrolyzations of other alkali metal or acid halides. U.S. Pat. No. 1,474,594, by way of particular note, is an early reference mentioning the passage of a mixture of air or oxygen over the surface of a conventional electrode. In the electrolysis of common salt brine, for example, the reaction at the depolarized cathodic oxygen electrode in the alkaline media of the catholyte is: EQU O.sub.2 +2H.sub.2 O+4e.sup.-.fwdarw. 4OH.sup.- with E.degree.=0.401 v.
In comparison, the cathode reaction in a traditionally conventional chlor-alkali cell is EQU 2H.sub.2 O+2e.sup.- .fwdarw.H.sub.2 +2OH.sup.- with E.degree.=-0.828 v.
Thus, the use of an oxygen gas bearing depolarized electrode for chlor-alkali electrolytic cells brings about a theoretically achievable electrical potential requirement saving of 1.229 volts. This, for practical purposes, translates to the possibility of very substantial reduction in and economization of power costs when reckoned from the basis of the usual relatively low voltages (frequently in the range of ca. 2 to 5 volts) at which a typical chlor-alkali diaphragm cell operates in order to effect the desired electrolysis and accommodate associated overvoltage requirements.
Nonetheless, there are certain difficulties involved in the heretofore known and applied use of porous electrodes. Besides ordinarily high cost, two of the more predominant and serious problems associated therewith are catalyst longevity and flooding. The latter phenomenon involves the deleterious liquid filling of all, or at least most, of the pores in the electrode structure with simultaneous corresponding exclusion of gas therein. This then effectively incapacitates the electrode and brings about loss of desired reaction occurrence therein and therewith. Several means and expedients have been utilized to avoid or overcome at least the flooding problem including wetproofing of at least a portion of the pores, porosity control and so forth. These, however, are oftentimes expensive and/or tedious and difficult to effectuate rendering them impractical despite their apparent value.
The basic characteristics and operational principles and limitations of porous electrode design and utilization practice are so widely comprehended by those skilled in the art that further elucidation thereof and elaboration thereon in unnecessary for thorough understanding and recognition of the advance contributed and made possible to achieve by and with the development(s) of the present invention.